1. Field Of The Invention
The present invention relates to a process for dyeing polyester fibers which have been modified so that they can be dyed with cationic dyes, and more particularly to a process for dyeing acid-modified polyester fibers a black color.
2. Description Of The Prior Art
Polyester fibers have been widely used as synthetic fibers for fiber goods because of their excellent properties, but it has been difficult to dye polyester fibers a clear and deep color.
Of various dyes, those dyes which give the most brilliant and deep color are cationic dyes for polyacrylonitrile fibers. For the purpose of dyeing polyester fibers also a brilliant and deep color, investigations have been made to render the fibers dyeable with cationic dyes. For example, Japanese Patent Publication No. 10497/1959 discloses a modification such as copolymerization using sulfoisophthalic acid as an acidic material as one approach toward rendering polyester fibers dyeable with cationic dyes.
However, when modified polyester fibers are dyed with dyes which have been widely used as cationic dyes for polyacrylonitrile, the exhaustion, particularly in black-dyeing, is so unsatisfactory that the fibers can not be dyed a deep black color. Furthermore, when blends or unions between the acid-modified polyester fibers and other fibers are dyed with conventional cationic dyes, staining of fibers other than the modified polyester fibers is observed remarkably.
Examples of commercially available black cationic dyes for polyacrylonitrile fibers are exemplified by the following dye combinations: ##SPC1##
In the above formulae, X.sup.- represents an anion such as Cl.sup.-
These mixed black dyes are very poor in exhaustion to polyester fibers, as described above, and thus do not result in a deep black color, and moreover a large degree of staining of other fibers which are present together with the polyester fibers results when these dyes are used.
Investigations have been made on a method for dyeing acid-modified polyester fibers a deep black color, and it has been found that deep black dyeings of extremely high color value can be obtained using a dye bath containing a specific combination of cationic dyes.